1. Field of the Invention
The present invention relates to an X-ray mask used for X-ray lithography and its fabrication method.
2. Description of the Prior Art
Conventionally, there have been used heavy metals such as Au, W, Ta as X-ray absorbers for X-ray masks. However, in using these heavy metals as X-ray absorbers, it was difficult to reduce the internal stress of each absorber. To solve the disadvantage, the present inventors have developed such an X-ray mask as shown in Japanese Patent Laid-open No. sho 63-232425, wherein a Ti--W alloy film is formed by sputtering at an atmosphere of an argon gas added with nitrogen. The above technique made it possible to form the film of the absorber low in the internal stress with high repeatability.
Incidentally, the X-ray absorber of the Ti--W alloy film previously proposed was low in internal stress; but had such a tendency that the crystal structure became columnar. For X-ray absorber having the columnar structure, the etching tends to proceed by each columnar unit. This causes a disadvantage in degrading the dimensional accuracy of the pattern.